A filter material with improved wettability and water-absorption is provided. The filter material is useful in making brewing bags/pouches, filters and the like.
In general, filter bags for cold- and hot-filtering procedures, for example tea bags, coffee bags (also see German Patent Document No. 39 02 298), filter bags for aromas, spices and cooking pouches, for example for rice and vegetables; filter papers for tea and coffee, for the beverage industry, for medical applications and oil and emulsion filtration, are made of heat-sealing and non-heat-sealing filter materials.
It is known in this respect that hydrophilic filter papers swell immediately upon contact with water, namely the paper strongly absorbs moisture and the paper fibers swell, and as a result the number of apertures between the fibers and the size of the apertures change.
As regards, for example, a tea bag filled with highly gas-generating herbs, medicinal plants or tea, the gas pressure so generated may even burst the bag when hot water is poured on it.
Moreover, the strongly hydrophilic action of such a hydrophilic material used to make tea or coffee bags may substantially reduce the time that the tea or coffee is in contact with the boiling water. As a result, the flavor of the coffee or tea and the entailed coloring are degraded.
German Patent Document No. 19 51 360.0 A1, for example, proposes solving this problem by using papers of large pore widths.
Another way to prevent moisture absorption by the paper fibers illustratively is to make them hydrophobic by means of a latex dispersion in the manner suggested in European Patent Document No. 0 632 163 A1, whereby the water absorption becomes practically nil.
However, this hydrophobic treatment incurs the drawback of substantially longer leaching of a tea bag so made on account of its water-repellant properties than is the case for an untreated, conventional bag.
A further drawback so incurred is that a tea bag which can be wetted only with difficulty on account of such treatment and over which is poured hot water, immediately after such pouring tends to float to the water surface. At this surface, however, the water temperature is known to be lower than at the middle and lower part of the container. Furthermore, with only part of the bag being surrounded by water, the leaching of the contents is decelerated.
The filtering time of the water in the filter may be raised to such an extent in a tea or coffee filter made of such a hydrophobically treated filter material that there is danger, where beverage machines are concerned, that the liquid will-overflow the filter.
Accordingly, it is the objective of the present invention to control the water-wettability and the water-absorption of the filter material., that is to appropriately treat this filter material, to achieve amphiphilic interaction between the hydrophobic and hydrophilic properties of the filter material in such a manner that, following manufacture into a brewing bag/pouch or a filter, the above cited drawbacks are precluded. Another objective of the present invention is a method for the manufacture of such a filter material.
Embodiments of the inventive filter material as well as methods of manufacture of such a filter material are described below and set forth in the claims.